Step 1
To make the rissoles, process the brioche in a food process or until fine breadcrumbs form. Transfer to a bowl. Add the onion, parsley, mozzarella, parmesan and garlic to food processor. Process until finely chopped. Add beef, egg, mustard and brioche breadcrumbs. Season. Process until just combined. Transfer to the bowl. Shape mixture into sixteen 1.5cm-thick patties. Transfer to a tray lined with baking paper. Place in the fridge until required.
Step 2
Preheat the oven to 210C/190C fan forced. Heat 1 tbsp oil in a flameproof, ovenproof casserole dish over medium-high heat. Cook rissoles, in batches, for 2-3 minutes each side or until browned. Transfer to a plate. Reduce heat to medium-low. Add onion. Cook, stirring, for 2-3 minutes or until softened. Add the passata and sugar. Bring to the boil. Simmer for 2 minutes. Return rissoles to the pan and bring to a simmer. Remove from heat.
Step 3
Combine garlic and remaining oil in a bowl. Add brioche and toss to coat. Season. Combine cheeses in a bowl. Sprinkle half of the cheese over the rissoles. Top with brioche and sprinkle with remaining cheese. Bake for 10-12 minutes or until melted and golden. Set aside for 10 minutes to cool slightly before serving.